1. Field of the Invention
The invention pertains to materials and methods for making heat resistant concrete, and more particularly for a spall-resistant and/or heat resistant concrete. The invention also relates to materials and methods for making high strength concrete.
2. Description of Related Art
In the 1990s, fires in concrete-lined tunnels created a situation of rapidly rising temperature. This rapid rise in temperature led to explosive spalling of large areas of concrete. Large falling concrete chunks proved to be almost as dangerous to trapped motorists as the smoke and fumes from the fires. More recently, the increased heat of vertical take-off and landing aircraft (F-35 and Osprey) have caused great concern that explosive spalling might endanger both crew and aircraft. The process of heat-induced spalling is relatively simple. When concrete is exposed to temperatures above the boiling point of water, moisture in the concrete turns to steam. If the temperature rises more rapidly than the steam can escape, rising pressure causes the concrete to spall. The heat from jet exhaust or vehicle fires is typically much greater (in the range of 1700 to 2000° F.) causing potentially explosive spalling.
Accordingly, there is a need for concrete having improved spalling resistance. There is also a need for concrete having improved compressive and flexural strength, as these properties control how much concrete must be used to support a given design load. Furthermore, given the present interest in reducing the carbon footprint of various manufacturing processes, there is a need for concrete formulations that reduce the production of carbon dioxide during cement making.
Modern concrete mixes typically contain various additives in addition to cement, water, and aggregate. Some familiar additives include ground blast furnace slag, coal ash, and expanded perlite. Expanded perlite is typically used as an additive primarily in lightweight applications to provide thermal barriers for fire protection. The perlite materials that are used are typically quite coarse and added in fairly large quantities. Water-to-cementitious contents are typically above 0.6 by mass and in most cases the material is being used as one of the fine aggregates. Coarse aggregates, as are normal in structural concrete, are not usually present. Some examples of concrete formulations include the following:
U.S. Pat. No. 7,748,453 to Reddy discloses a method of making a wellbore fluid comprising a cement composition that contains cement, ground expanded perlite at 1-100 percent and 2-400 μm size, and water.
U.S. 2011/0100626 to Brenneis et al. discloses a method of making a sellable wellbore fluid composition containing ground unexpanded perlite of 1-100 μm size and 1-75 percent composition; additional components include fly ash, slag cement, metakaolin, and fumed silica.
U.S. Pat. No. 5,114,617 to Smetana et al. discloses a concrete composition that contains 8-65 percent cement, 0.5-20 percent smooth surfaced expanded perlite, less than 0.15-0.6 mm, and may contain fly ash.
U.S. 2009/0011207 to Dubey discloses a lightweight cementitious slurry of 35-60 percent Portland cement, 2-10 percent expanded, chemically coated perlite and at least one of silica fume, metakaolin, blast furnace slag, fly ash as mineral additive; fly ash can be 10-60 percent.
U.S. 2011/0155019 to Albright et al. discloses a cement blend with Portland cement, 0.1-7 percent perlite, 0.1-40 percent fly ash.
U.S. Pat. No. 5,294,255 to Smetana et al. discloses a grout composition with expanded perlite, Portland cement, and fly ash.
U.S. Pat. No. 7,736,431 to Bui discloses a lightweight concrete mix with expanded perlite in the 1-2.5 mm size range.
U.S. Pat. No. 6,402,830 to Schaffer discloses a lightweight concrete composition with pumice and 1-4 percent expanded perlite at minus 3/16 inch to dust in size.
U.S. Pat. No. 5,356,446 to Smetana et al. discloses a cementitious compound with expanded perlite at 100-30 mesh and 10-20 percent.
U.S. Pat. No. 4,963,191 to LaFleur discloses a cementitious composition with Portland cement and expanded perlite.
U.S. Pat. No. 4,210,457 to Dodson et al. discloses a fly ash and Portland cement mixture with expanded perlite.
U.S. Pat. No. 2,853,394 to Riddell et al. discloses that expanded perlite is 300 μm size and 1-3 percent of admixture.
U.S. Pat. No. 7,748,453 to Reddy et al. discloses the use of perlite additive in fairly large amounts for use in flowing non segregating grouts.
U.S. 2011/0155019 to Albright et al. discloses the use of perlite additive. Silica fume is required as are hollow microspheres and titanium oxide. High temperature resistance and strength enhancement are reported benefits. The disclosure includes an OC blend of fused silica, micro-beads, ground expanded perlite, fumed silica, and class C fly ash used with cement and additional C fly ash, ground expanded perlite, and aggregates for a moderate weight concrete for fire performance. High temperature concrete used OC formulation which has a large amount of additional additives including vinyl acrylic copolymer, acrylic latex, and TiO2.
3. Objects and Advantages
Objects of the present invention include the following: providing a structural concrete with improved heat resistance; providing a structural concrete with improved spalling resistance; providing a structural concrete with improved strength; providing a structural concrete with improved resistance to chloride ion penetration; providing a concrete additive that reduces the amount of carbon dioxide generated in manufacture; providing a concrete additive that reduces the amount of Portland cement needed; and providing a concrete additive that improves the strength, heat and spalling resistance, and resistance to chloride ion penetration of structural concrete. These and other objects and advantages of the invention will become apparent from consideration of the following specification, read in conjunction with the drawings.